55 Ocular Signs and Symptoms Elicited by a Naturalistic Allergen Challenge in an Environmental Exposure Chamber Model Versus a Direct Allergen Instillation Model

BACKGROUND: Direct-instillation ocular models are well established for eliciting allergic responses in research and clinical testing. This study compared direct ocular instillation of allergen to a more naturalistic airborne allergen exposure. METHODS: Thirteen subjects with histories of ragweed allergy and positive skin prick responses attended screening, dose-finding, dose, confirmation, and analysis study visits. For conjunctival allergen provocation testing (CAPT), 1 drop of ragweed allergen was administered to each eye, at the lowest possible subject-specific concentration between 1.6 and 100 protein nitrogen units per 25 μl drop. For environmental exposure chamber (EEC) testing, subjects were exposed to continual airborne ragweed pollen at 3500 ± 500 particles/m(3). Symptoms of itching and tearing were self-assessed on diary cards by subjects. Signs of hyperemia, swelling, and mucous discharge were assessed by clinicians. Assessment time points started at 30 minutes before exposure and continued through 180 minutes after exposure. RESULTS: At baseline, there were minimal signs and symptoms. Maximum mean hyperemia with CAPT was 2.3 ± 0.6 units (between moderate and severe) and with EEC was 1.9 ± 0.5 units (approximately moderate); these maxima occurred after 30 minutes with CAPT (rapid spike) and after 180 minutes with EEC (gradual increase). Mean swelling was <1 unit out of 4 units at all times (CAPT and EEC), and mucous discharge was observed in only 1 subject during the study (with CAPT). Maximum mean itching with both CAPT and EEC was 2.8 ± 1.0 units (approximately severe), but this maximum occurred after 20 minutes with CAPT (rapid spike) and after 180 minutes with EEC (gradual increase). Maximum mean tearing with CAPT was 1.2 ± 0.7 units (approximately mild) and with EEC was 1.6 ± 0.6 units (between mild and moderate); these maxima occurred after 15 minutes with EEC (rapid spike) and after 120 minutes with EEC (gradual increase). CONCLUSIONS: The time courses of allergic signs and symptoms differed between CAPT and EEC models; however, both models evoked similar maximum response levels. This demonstrates that the EEC model is a useful challenge model for mimicking natural airborne ocular allergen exposure.